Electrical timing apparatus and means for adjusting the same



Nov. 9,

W. CHILDERS ELECTRICAL TIMING APPARATUS AND MEANS FOR ADJUSTING THE SAMEFiled July 3, 1961 n\ J0ID L (1F) 39 3m I 50 N32 H- 33 ll Warr en("/W/aers IN VEN TOR.

ATTORNEY United States Patent 3.217 206 ELECTRICAL THMKNG AP PARATUS ANDlJIEANS FOR ADJUSTING THE SAME Warren Childers, 1723 Marshall St.,Houston, Tex. Filed July 3, 1961, Ser. No. 121,641 Claims. (Cl. 315-129)This invention relates to timing mechanism and more particularly to anelectrical circuit for controlling the timing of electrically operatedapparatus and means for accurately adjusting the functioning of such acircuit.

The invention is capable of wide application for the timing of theopening and closing of electrical circuits for various purposes, andfinds particular utility in connection with the timing of photographicexposures.

The present invention has for an important object the provision ofelectrical timing mechanism which is accurate and dependable inoperation and in which means is provided for restoring the accuracy oftiming in the event that some characteristic of the circuit should bevaried or some component of the same replaced.

Another object of the invention is to provide an electrical timingcircuit which is adjustable and in which capacity, voltage and rate ofcurrent discharge may be utilized to determine the interval of timethrough which the circuit operates.

A further object of the invention is the provision of an electricaltiming circuit which depends for its operation upon the conductingcharacteristics of a vacuum tube and which employs audible means foradjusting the voltage at which such a tube conducts.

Another object of the invention is to provide electrical timingmechanism of the kind referred to which may be used for the timing ofphotographic exposures and in Which means is embodied for automaticallyvarying the time of exposure in accordance with the intensity of thelight source used for the exposure.

The above and other important objects and advantages of the inventionmay best be understood from the following detailed descriptionconstituting a specification of the invention, reference being had tothe annexed drawings illustrating a preferred embodiment of the same.

In the drawings, FIGURE 1 is a circuit diagram of the timing mechanismof the invention; and

FIGURE 2 is a diagram illustrating the operational characteristics ofthe vacuum tube employed in the mechanism of the invention and how thecircuit may be adjusted.

Referring now to the drawings in greater detail, the invention isillustrated herein in connection with its use in the timing ofphotographic exposures making use of filters of different color, orhaving different light transmitting properties, and in accordance withthe density of the photographic transparency being used.

The timing mechanism of the invention includes a thyratron tube V ofconventional type into the control grid circuit of which a photoelectriccell is connected. The tube V is of a well known type having a cathode14a, control grid 2, suppressor grid 2a and a plate 26.

The voltage supply circuit of the control grid 2 of the tube V, includesthe photo cell 15, source of current 16, and condensers 10, L2 and 14 ofa condenser system preferably in an adjustable decade arrangement. Thus,the voltage applied to the control grid 2 will be the voltage across thedecade condenser system plus the voltage of the supply source 16.

A charging circuit is provided for the decade condenser system, whichincludes the primary direct current voltage supply source 5, voltageregulating tube 35, adjustable resistor 8 having a slider 12, apotentiometer 7 having a slider 11 and a fixed resistor 6. The chargingcircuit also includes an auxiliary direct current voltage supply source9 having a potentiometer it which may be connected in circuit with thecondenser system through relay contacts 3 and 4 and with the source 5through slider 11. By this arrangement the decade condenser system maybe charged at any desired voltage.

A relay R1 is provided having a moving contact 3 and a stationarycontact 4, by which the charging of the condensers is elfected. Thus,when the contact 3 is in engagement with contact 4, the condensercharging circuit is closed, and when contact 3 is out of engagement withcontact 4 the charging circuit is open.

The relay R1 is operated from the same current source 40 through thestationary contact 22 and movable contact 21 of plate relay R2 throughcoil of R1 either through a momentary contact switch 1% or throughstationary contact 24 and movable contact of the relay R1. Thus, uponenergization of the coil 20 by momentary closing of the switch 19, themoving contact 25 is brought into engagement with contact 24 and held insuch contact to keep coil 20 energized during a timing interval of theequipment.

The timing equipment is provided with output connections 42 and 44 for acircuit into which equipment such as a light source may be connected.Output contacts 12 and 44 are energized from the source as directly tocontact 44 and from contact 42 through stationary contact 24, movablecontact 25 back to the source.

In FIGURE 1, the circuit is in the non-timing state. During thiscondition negative voltage is supplied from a suitable source of supplysuch as the battery 5 or other power supply circuit, to the adjustablecapacitors 410, 12 and 14 to the thyratron control grid 2 through relaycontacts '3 and 4. The amplitude of the negative voltage is determinedby the voltage supply source 5 by the adjustment of a voltage dividingnetwork including resistors 6, 7 and 8, the resistor 7 being adjustableby a slider 11 and the resistor 8, being adjustable by a slider 12 andby an auxiliary voltage supply source 9 and a voltage dividing circuitassociated therewith which includes the variable resistor 10a providedwith a slider 13. The adjustable voltage network may be calibrated torepresent photographic density, the resistor 7, for example, beingcalibrated in increments of .10 of photographic density and the resistor8 being then calibrated in increments of .01 of photographic density.Slider 11 is used for coarse adjustment of voltage and slider 12 is usedfor fine adjustment. (In the example given above, resistance 7 isdivided for .10 increments of density and resistance 8 is divided for.01 increments of density.) Negative supply 9 is adjusted by means ofresistance 11):: and slider .13 to add (to voltage appearing at slider11) negative voltage almost equal to the critical control grid potentialof the thyratron. This critical control grid potential is the negativecontrol-grid voltage required to prevent the thyratron from firing whenthe peak valve of the positive A.C. half-cycle appears at its plate.This adjustment is necessary in order to establish the cathode 14a aszero voltage reference for both the voltage divider 6, 7 and 8 and thecapacitors 1t 12 and 14.

Charging of the capacitors is completed within a very short time aftercontact is made through relay points 3 and 4. After the capacitors arecharged current in the photoelectric tube circuit flows from battery 16through tube 15, contacts 3 and 4-, slider 13, part of the resistor 10a,part of resistor 7 depending upon the position of slider 11, and throughresistor 6 back to the battery 16. Since the phototube 15 is usuallylocated in a position remote from the rest of the circuit by means of aflexible cable, the capacitance of the phototube and of its connectingcable 1a becomes a factor affecting time.

This capacitance has the same effect as would a capacitor added to theadjustable capacity system 10, 12 and 14 and produces a constant errorin the time unit system. This error in a 1000 to 1 capacity decadesystem may amount to approximately of a single unit and may be correctedby using a smaller value capacitor at the single unit position. On unitsettings above 10, the error will then become less than 1%.

In other circuits the phototube is sometimes connected to relay point 17instead of at the grid line 13; thus the phototube and voltage supply 16are out of the circuit when in its non-timing state. However, thisarrangement produces an inconstant error in timing because of thecapacity which is left in the phototube cable at the end of a timeinterval. Immediately following a time cycle, this cable capacity beginsto drain off through the leakage path provided by the phototube and mayrequire several seconds or even minutes to drain completely. Thereforethe succeeding time cycle will be affected by the quantity of currentstill left in the cable and the error will vary with the time elapsedsince the last timing cycle and with the volume of light falling uponthe phototube. In FIGURE 1 the phototube is connected so as to produce aconstant error which may be compensated rather than a variable errorwhich may not be compensated.

The timing cycle is begun by momentarily depressing switch 19 whichsupplies current to the power relay 20. The other side of the A.C.potential is supplied through contacts 21 and 22 of the plate relay R2.Contacts 24 and 25 of the power relay form an electrical latch tomaintain the current supply to the power relay R1 after the momentarycontact switch 19 is released. When the power relay is energized, theelectrical contact between relay points 3 and 4 is broken and currentbegins to flow from the selected one of the capacitors 10, 12 and 14,through the phototube and to the positive potential of voltage supply16. As this current fiow continues, the grid 2, which monitors thecapacitor voltage, becomes progressively less negative with respect tothe cathode until the control grid becomes less negative than requiredto prevent the thyratron from firing. The first positive half-cycle ofthe AC. supply which appears at the plate 26 of the thyratron after thiscritical control grid potential is passed will cause the thyratron tofire, energizing the plate relay R2 and breaking the electrical contactbetween points 21 and 22 of the plate relay R2. Interruption of theelectrical contact between points 21 and 22 of the plate relay breaksthe current supply to the power relay R1 causing the electrical latchbetween points 24 and 25 to be released and the points 3 and 4 toremake. When points 3 and 4 remake suflicient negative grid potential issupplied at the control grid 2 to prevent the thyratron from firing onthe following positive half-cycles of the AC. supply. The selected oneof the capacitors 10, 12 and 14 is then recharged and the circuit isagain ready for a repeat timing cycle. The time interval in theoperation of this circuit is the product of the capacity placed in thecircuit, the voltage impressed upon the capacity and the rate of currentflow through the phototube. Important constants in the circuit areamplitude of the peak A.C. positive half cycle and the negative voltagebetween points 13 and 11 of the condenser charging circuit (FIGURE 1).As shown in FIGURE 2, these two voltage values are interdependent. Theymust be stable and carefully adjusted if optimum accuracy is to berealized from the voltage divider comprised of resistors 6, 7 and 8. Ina practical circuit, the constant peak A.C. positive half-cycle isestablished by the use of a voltage regulating transformer in the A.C.supply. The remaining constant (negative voltage between points 11 and-13 in FIGURE 1) is then dependent only upon the characteristic of thethyratron tube employed in the circuit. Tube characteristics varybecause of manufacturing tolerances. With a maximum anode potential of160 volts as illustrated in FIGURE 2, a particular tube type 4t (2D21)will have a critical grid (firing) voltage between -l%. and 2 /2 volts.It is important for the negative voltage supply 9 to exceed 2 /2 voltsto be adequate for normal manufacturing tolerances of this tube type.

The critical nature of the voltage adjustment between points 1 1and 13may be appreciated by considering the voltage requirements of a densitycalibration system covering a density range of 2.10 to 00 or a ratio of125.9 to 1.0. The amplitude of voltage supplied from supply 5 iscontrolled and regulated by the voltage regulator tube 35 and is limitedto approximately 108 volts. Thus, the minimum voltage setting of voltagenetwork including resistors 6, 7 and 3 would be 108/126 or .8571 voltand the next higher increment of change (+.01 density) would increasethis value by approximately 2.3% or to .8768 volt.

Due to the critical exposure requirements encountered in the graphicarts field, it is essential that this calibration (adjustment of slider13) be made with extreme accuracy. This problem is complicated by thefact that commercial versions of the circuit described in FIGURE 1 willordinarily be used by workers who have little or no knowledge ofelectronics and do not have access to precision electronic measuringdevices. In order to overcome this problem, a simple audible calibrationsystem was devised. A switch 36 was added to the circuit for the purposeof shunting resistance 6 to the cathode. By sliding slider 11 toposition 37, all of the voltage from supply 5 is removed from thecircuit. The negative voltage remaining on the control grid 2 is thensupplied entirely from supply 9. The resistance 38 has previously beenadjusted to prevent relay 23 from pulling in at anode potentials of lessthan a critical value (in this case (FIGURE 2) 14-0 volts). In FIGURE 2,dotted line 31 begins at a point where the volt line intersects thepositive half of the A0. sine wave. This point represents the minimumpull-in voltage required by the plate relay R2 and its value isdependent upon the series resistance adjusted at 38. Following line 31down into the critical control grid potential segment it will be foundto intersect the critical control grid curve at a control grid voltageof approximately 1.9 volts (3 1). This is the control grid voltage whichwould just allow the thyratron to fire at the same instant the amplitudeof the anode potential reached the critical pull-in value of the platerelay R2. After the relay armature is pulled in it requires less voltagethan the critical pull-in voltage to maintain its in position;therefore, it will remain in for a time represented by line 32 drawnbetween lines 31 and 39. When the amplitude of the positive half cyclereaches the point intersected by line 39 the relay R2 armature returnsto its relaxed position. If the control grid voltage were increased by.05 volt as in 29, the effect would be to shift conduction point of thethyratron to a point represented by line 40. Such a shift creates adecided difference in sound since the relay armature is in for a shorterlength of time. The addition of another .05 volt control grid potentialwould prevent the thyratron from firing. Beginning with a control gridpotential of 2.6 v. as at 27 and gradually reducing this by means ofslider 13, there is, first, no sound, then an erratic sound which is dueto the slight 1%) variation of the peak anode potential, and then quitesuddenly there is heard a steady 60 cycle buzz. There is no furtherSound change at control grid potentials less than 34 even though thethyratron fires earlier because the relay R2 pull-in point is determinedby its own critical pull-in voltage rather than the firing point of thethyratron.

As is well known, the density of a photographic image may be expressedas a logarithmic function and the photographic exposure required variesas the reciprocal of the photographic transmission.

By the use of the decade capacity system in the timing circuit, asdescribed above, and including the voltage dividing system having thevariable resistors 7 and 8, which may be adjusted in accordance with alogarithmic scale, the condenser system may be made to vary as alogarithmic function, so that the voltage supplied to the capacitors maybe made to vary in proportion to the antilog of the photographicdensity.

It will thus be seen that the invention, constructed and operated asdescribed above, provides electrical timing mechanism which is extremelyaccurate by which the timing of various devices can be regulatedthroughout a wide range, and Which may be easily and accurately adjustedto compensate for variations in vacuum tube characteristics.

The invention is disclosed herein in connection with a certain specificembodiment of the same, but it will be understood that this is intendedby way of illustration only, and that numerous changes in the electricalcomponents and circuits may be made, within the spirit of the inventionand the scope of the appended claims.

Having thus clearly shown and described the invention, what is claimedas new and desired to secure by Letters Patent is:

1. In electrical timing mechanism a gas thyratron tube having a plate, acontrol grid, and a cathode, a control grid bias circuit including aprimary current voltage source, an auxiliary direct current voltagesource, first means for adjustably producing a bias voltage from saidprimary direct current voltage source, second means for adjustablyproducing a bias voltage from said auxiliary direct current voltagesource, said first and second means being connected in series in saidcontrol grid bias circuit between cathode and grid, and a condenserconnected between cathode and control grid paralleling said first andsecond means, a charging circuit for said condenser including said firstand second means and said primary and auxiliary direct current voltagesources, means for opening and closing said charging circuit, saidlatter means being positioned in the charging circuit at a point todisconnect said first and second means and said primary and auxiliarydirect current voltage sources from the control grid bias circuit uponopening of the charging circuit, a plate circuit, a source ofalternating current in the plate circuit, audible sound producing meansincluding an electromagnetic coil in said plate circuit for producing anaudible signal of predetermined frequency upon energization of said coilwhen the current in said plate circuit reaches a predetermined value,and means for shunting said first means and said primary direct currentvoltage source out of said control grid circuit whereby said secondmeans may be adjusted to select a critical control grid bias voltagesetting which critical bias voltage setting is determined by an operatorwhen a predetermined audible sound is produced by said audible soundproducing means.

2. The apparatus set forth in claim 1 together with a dischargingcircuit for said condenser, and means in said discharging circuitresponsive to light intensity for controlling the discharging of thecondenser.

3. The apparatus as set forth in claim 2 wherein said first meansincludes a voltage divider network which is adjustable tologarithmically vary the charge of said condenser proportionate to theanti log of a predetermined photographic density.

4. The timing mechanism as set forth in claim 1 wherein said audiblesound producing means is an electromagnetic relay capable of buzzing atthe frequency of said alternating current source.

5. The apparatus as set forth in claim 1 wherein said means for openingand closing said charging circuit includes an electromagnetic powerrelay having a first set of switch contacts in said charging circuit, asecond set of switch contacts and an electromagnetic coil, a timinginterval initiating circuit, including said alternating current source,a normally open momentary contact switch and said power relay coil, anelectrical latch for said power relay including said second set ofswitch contacts, said electrical latch being adapted to hold said powerrelay energized when said momentary contact switch is momentarily closedand subsequently released, a load circuit in circuit with said secondset of switch contacts and said alternating current source, which isenergized when said second set of switch contacts is closed, and meansresponsive to the energization of said electromagnetic coil in saidplate circuit for de-energizing said power relay.

References Cited by the Examiner UNITED STATES PATENTS 2,238,987 4/41Albin 317142 2,420,887 5/47 Lane 315-360 2,473,640 6/49 'Faulk 315-360 X2,658,141 11/53 Kurland 315-456 X 2,785,346 3/57 Large 315-360 2,941,1276/60 Elliot 317-142 GEORGE N. WESTBY, Primary Examiner.

ARTHUR GAUSS, Examiner.

1. IN ELECTRICAL TIMING MECHANISM A GAS THYRATON TUBE HAVING A PLATE, ACONTROL GRID, AND A CATHODE, A CONTROL GRID BIAS CIRCUIT INCLUDING APRIMARY CURRENT VOLTAGE SOURCE, AN AUXILIARY DIRECT CURRENT VOLTAGESOURCE, FIRST MEANS FOR ADJUSTABLY PRODUCING A BIAS VOLTAGE FROM SAIDPRIMARY DIRECT CURRENT VOLTAGE SOURCE, SECOND MEANS FOR ADJUSTABLYPRODUCING A BIAS VOLTAGE FROM SAID AUXILIARY DIRECT CURRENT VOLTAGESOURCE, SAID FIRST AND SECOND MEANS BEING CONNECTED IN SERIES IN SAIDCONTROL GRID BIAS CIRCUIT BETWEEN CATHODE AND GRID, AND A CONDENSERCONNECTED BETWEEN CATHODE AND CONTROL GRID PARALLELING SAID FIRST ANDSECOND MEANS, A CHARGING CIRCUIT FOR SAID CONDENSER INCLUDING SAID FIRSTAND SECOND MEANS AND SAID PRIMARY AND AUXILIARY DIRECT CURRENT VOLTAGESOURCES, MEANS FOR OPENING AND CLOSING SAID CHARGING CIRCUIT, SAIDLATTER MEANS BEING POSITIONED IN THE CHARGING CIRCUIT AT A POINT TODISCONNECT SAID FIRST AND SECOND MEANS AND SAID PRI-